On Sat, Oct 8, 2016 at 7:25 AM, Watson Ladd <watsonbl...@gmail.com> wrote:
> On Fri, Oct 7, 2016 at 3:04 PM, Eric Rescorla <e...@rtfm.com> wrote: > > > > > > On Fri, Oct 7, 2016 at 3:00 PM, Ilari Liusvaara < > ilariliusva...@welho.com> > > wrote: > >> > >> On Fri, Oct 07, 2016 at 01:41:14PM -0700, Watson Ladd wrote: > >> > On Fri, Sep 23, 2016 at 10:47 PM, Ilari Liusvaara > >> > <ilariliusva...@welho.com> wrote: > >> > > > >> > > Also, it is very likely that 0-RTT would need its own read API, > >> > > because > >> > > it is pretty unlikely that existing API could be safely retrofitted > >> > > or even purpose-built unified API be designed that isn't just asking > >> > > for security problems via mixing 0-RTT and 1-RTT data. > >> > > >> > Yes. In particular I think the TLS state machine transitions need to > >> > be ordered with respect to the arrival and sending of data. The > >> > challenge for a multithreaded program (yes, some programs have > >> > multiple threads sending and receiving at once) is making this make > >> > sense, or even a single-threaded program where the TLS stack can > >> > change state at times not visible to the sending thread. Maybe there > >> > is some slop here, like 0-RTT can become 1-RTT on send, but this > >> > raises all sorts of problems for receiving. I think we need to require > >> > separation in the API. > >> > >> 0-RTT can't be allowed to become 1-RTT on send (unless it is auto- > >> retransmit, which needs to be disableable, as sometimes that just plain > >> won't work). > > > > > > Can you explain why that is? > > Grammar problems. > > Let's say you have an context-free parseable protocol, and you want to > insert the restriction that there is a 0-RTT set of allowed constructions > and an 1-RTT allowed set that is bigger. The most obvious way to do this is > to treat the transition as a token that comes between the top-level > productions of each set of allowable things: so I send you a bunch of 0-RTT > allowed bits, then switch, then a bunch of 1-RTT allowed bits. > > If the sending stack can insert that transition anywhere the grammar > explodes. > In the APIs people have been designing, 0-RTT can become 1-RTT but not the other way around. Specifically: - There is an option to allow 0-RTT writing - With that option on, SSL_Write() succeeds in both 0-RTT and 1-RTT modes. - There is a callback that tells you when you have gone from 0-RTT to 1-RTT. -Ekr One could try to handle this by some nasty "did we switch before now" > construction to delay the transition. But you still need to switch how you > are reading. > -Ekr > > > > -Ekr > > > > > > > >> This impiles that the application always needs to explicitly signal > >> the end of 0-RTT data, even just to abort sending it. > >> > >> > > (This is the reason one needs to be especially careful when > combining > >> > > dynamic client certificates with HTTP/2... Basically, it can not be > >> > > done safely without coordination on application layer). > >> > > > >> > > One likely wants application protocol to be able to specify part of > >> > > or the entiere request context and to extract that part in the other > >> > > end when requesting a certificate selection. This is to allow > putting > >> > > part of coordination data into the request itself. However, this is > >> > > not > >> > > sufficient for e.g. HTTP/2 signaling, so more needs to be exchanged > at > >> > > application layer. > >> > > > >> > > And then upon completion of the authentication (either successful or > >> > > explicitly rejected), signal the application with the new > certificate > >> > > chain and the context the request had. > >> > > >> > This is going to require major changes to APIs and to the HTTP/2 > >> > layer. It also interacts with token binding, whee! My question then > >> > becomes one of what we actually need: can we assume that leakage > >> > between authentication contexts over a single session is safe because > >> > all contexts represent the same principal, by restricting the usages, > >> > or is this overly restrictive? > >> > >> Yes, it is going to reuqire such changes. > >> > >> And you absolutely can not assume that all contexts present the same > >> principal. > >> > >> And as I said, in multiplexed protocol like HTTP/2, you need > application- > >> level coordination on top. TLS just can't do that. > >> > >> > When we have multiple requests and replies in flight and the > >> > authentication state changes, things get nasty. If we think of TLS as > >> > sending a stream of events including authentication changes to the > >> > application, this fits the semantics of the TLS draft as I understand > >> > them to be, but does not necessarily fit what application protocols > >> > want. There might be a semantic mismatch here requiring reworking of > >> > one or another part. > >> > >> Also, some applications presumably want the events done synchronously, > >> so they don't move with data reads. > >> > >> > >> Basically, post-handshake auth is heckuva nasty problem. > >> > >> > >> -Ilari > >> > >> _______________________________________________ > >> TLS mailing list > >> TLS@ietf.org > >> https://www.ietf.org/mailman/listinfo/tls > > > > > > -- > "Man is born free, but everywhere he is in chains". > --Rousseau. >
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